Pathology peer review as carried out by the Natioal Toxicology Program (NTP) has become a standard means of assuring the validity of the pathology data generated in the rodent bioassays. A major portion of the NTP effort in this regard is contained in the contract for pathology quality assurance. "Pathology support for the NTP-Quality Assurance" (QA). Under this contract, pathology materials (slides, blocks, etc.) are evaluated for quality (staining, etc.) and integrity (slide, block match, presence of tissues, etc.). Also, the pathology diagnosis for most in- house studies and all NTP studies carried out in the laboratories under contract to the NTP are verified by a second pathologist. Currently, the pathology tables are received electronically and formatted for use by the QA pathologists. All discrepancies between the study pathologist and the QA pathologists are highlighted in a QA narrative which is submitted together with the slides to the NTP. The discrepancies are evaluated by the Pathology Working Group (PWG) chairperson who is responsible for selecting representative cases for PWG review. The QA Pathologist and other Experts participate in the PWG Peer Review where selected cases are examined without knowing either the study or QA Patholgists diagnosis.